SIGNAL PROCESSING APPARATUS

• US 20090099430A1
• Filed: 12/19/2008
• Published: 04/16/2009
• Est. Priority Date: 03/07/1991
• Status: Active Grant

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Weber, Walter M., Diab, Mohamed K., Kiani-Azarbayjany, Esmaiel
• Granted Patent: US 7,937,130 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: G06F 2218/04 Denoising
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H

Abstract

A signal processor which acquires a first signal, including a first primary signal portion and a first secondary signal portion, and a second signal, including a second primary signal portion and a second secondary signal portion, wherein the first and second primary signal portions are correlated. The signals may be acquired by propagating energy through a medium and measuring an attenuated signal after transmission or reflection. Alternatively, the signals may be acquired by measuring energy generated by the medium. A processor of the present invention generates a primary or secondary reference signal which is a combination, respectively, of only the primary or secondary signal portions. The secondary reference signal is then used to remove the secondary portion of each of the first and second measured signals via a correlation canceler, such as an adaptive noise canceler, preferably of the joint process estimator type. The primary reference signal is used to remove the primary portion of each of the first and second measured signals via a correlation canceler. The processor of the present invention may be employed in conjunction with a correlation canceler in physiological monitors wherein the known properties of energy attenuation through a medium are used to determine physiological characteristics of the medium. Many physiological conditions, such as the pulse, or blood pressure of a patient or the concentration of a constituent in a medium, can be determined from the primary or secondary portions of the signal after other signal portion is removed.

Claims

1. A method determining a value of blood oxygen saturation of pulsing blood, the method comprising:

receiving three or more intensity signals from at least one light-sensitive detector which detects light attenuated by body tissue carrying pulsing blood, wherein the three or more intensity signals correspond to detection of at least three wavelengths of the light; and

determining a value of oxygen saturation using the three or more intensity signals, wherein the three or more intensity signals include motion induced noise.

2. The method of claim 1, wherein the step of determining further comprises processing at least two of the three or more intensity signals with an adaptive algorithm.

3. The method of claim 2, wherein the adaptive algorithm comprises a least squares algorithm.

4. The method of claim 3, wherein the least squares algorithm comprises a least squares lattice.

5. The method of claim 1, wherein the step of determining further comprises processing at least two of the three or more intensity signals with a least squares algorithm.

6. The method of claim 1, wherein one of the three or more intensity signals corresponds to one of the at least three wavelengths and is used primarily to reduce an effect of the motion induced noise on the value of oxygen saturation.

7. The method of claim 6, wherein two of the three or more intensity signals correspond to two of the at least three wavelengths and are used primarily to determine the value of oxygen saturation.

8. The method of claim 1, wherein absorption coefficients associated with two of the at least three wavelengths are related to one another.

9. The method of claim 8, wherein absorption coefficients associated with two of the at least three wavelengths are proportional to one another.

10. The method of claim 8, wherein absorption coefficients associated with two of the at least three wavelengths are linearly proportional to one another.

11. The method of claim 1, wherein absorption coefficients associated with the at least three wavelengths are proportional to one another.

12. The method of claim 1, wherein each of the three or more intensity signals includes a signal portion and a noise portion, and wherein a non-zero reference signal corresponds to the noise portion of one of the three or more intensity signals.

13. The method of claim 1, wherein each of the three or more intensity signals includes a signal portion and a noise portion, and wherein a non-zero reference signal corresponds to the signal portion of one of the three or more intensity signals.

14. The method of claim 1, wherein the pulsing blood comprises arterial blood.

15. The method of claim 1, wherein the pulsing blood comprises venous blood.

16. A method of reducing an effect of motion induced noise on a plurality of intensity signals during the determination of a parameter of pulsing blood, the method comprising:

receiving a plurality of intensity signals from at least one light-sensitive detector which detects light of a plurality of wavelengths attenuated by body tissue carrying pulsing blood; and

processing one of the plurality of intensity signals using data from an additional intensity signal other than the plurality of intensity signals, the additional intensity signal corresponding to an additional wavelength of light, wherein the processing determines a value of blood oxygen saturation of the pulsing blood during motion induced noise, wherein the data from the extra wavelength is used to reduce an effect of the motion induced noise.

17. The method of claim 16, wherein the step of processing further comprises processing the plurality of intensity signals with an adaptive algorithm.

18. The method of claim 17, wherein the adaptive algorithm comprises a least squares algorithm.

19. The method of claim 18, wherein the least squares algorithm comprises a least squares lattice.

20. The method of claim 16, wherein absorption coefficients associated with the plurality of intensity signals are related to one another.

21. The method of claim 20, wherein absorption coefficients associated with the plurality of intensity signals are proportional to one another.

22. The method of claim 20, wherein absorption coefficients associated with the plurality of intensity signals are linearly proportional to one another.

23. The method of claim 16, wherein absorption coefficients associated with the plurality of intensity signals and the additional intensity signal are proportional to one another.

24. The method of claim 16, wherein the plurality of intensity signals and the additional intensity signal each includes a signal portion and a noise portion, and wherein a non-zero reference signal corresponds to the noise portion of one of the intensity signals.

25. The method of claim 16, wherein the plurality of intensity signals and the additional intensity signal each includes a signal portion and a noise portion, and wherein a non-zero reference signal corresponds to the signal portion of one of the intensity signals.

26. The method of claim 16, wherein the pulsing blood comprises arterial blood.

27. The method of claim 16, wherein the pulsing blood comprises venous blood.

28. A physiological monitor for determining a physiological parameter of a patient, the physiological monitor comprising:

an input which receives three or more intensity signals from at least one light-sensitive detector which detects light attenuated by body tissue carrying pulsing blood, wherein the three or more intensity signals correspond to detection of at least three wavelengths of the light; and

a processor which determines a value of oxygen saturation using the three or more intensity signals, wherein the three or more intensity signals include motion induced noise.

29. The physiological monitor of claim 28, wherein the processor processes at least two of the three or more intensity signals with an adaptive algorithm.

30. The physiological monitor of claim 29, wherein the adaptive algorithm comprises a least squares algorithm.

31. The physiological monitor of claim 30, wherein the least squares algorithm comprises a least squares lattice.

32. The physiological monitor of claim 28, the processor processes at least two of the three or more intensity signals with a least squares algorithm.

33. The physiological monitor of claim 28, wherein one of the three or more intensity signals corresponds to one of the at least three wavelengths and wherein the processor uses the one intensity signal primarily to reduce an effect of the motion induced noise on the value of oxygen saturation.

34. The physiological monitor of claim 33, wherein two of the three or more intensity signals corresponds to two of the at least three wavelengths and wherein the processor uses the one intensity signal primarily to determine the value of oxygen saturation.

35. The physiological monitor of claim 28, wherein absorption coefficients associated with two of the at least three wavelengths are related to one another.

36. The physiological monitor of claim 35, wherein absorption coefficients associated with two of the at least three wavelengths are proportional to one another.

37. The physiological monitor of claim 35, wherein absorption coefficients associated with two of the at least three wavelengths are linearly proportional to one another.

38. The physiological monitor of claim 28, wherein absorption coefficients associated with the at least three wavelengths are proportional to one another.

39. The physiological monitor of claim 28, wherein each of the three or more intensity signals includes a signal portion and a noise portion, and wherein a non-zero reference signal corresponds to the noise portion of one of the three or more intensity signals.

40. The physiological monitor of claim 28, wherein each of the three or more intensity signals includes a signal portion and a noise portion, and wherein a non-zero reference signal corresponds to the signal portion of one of the three or more intensity signals.

41. The physiological monitor of claim 28, wherein the pulsing blood comprises arterial blood.

42. The physiological monitor of claim 28, wherein the pulsing blood comprises venous blood.